Known vacuum interrupters can be used for medium voltage circuit breakers for applications in the range between 1 and 72 kV of a high current level. These circuit breakers are used in electrical networks to interrupt short circuit currents as well as load currents under difficult load impedances. The vacuum interrupter interrupts the current by creating and extinguishing the arc in a closed vacuum container. Modern vacuum circuit breakers tend to have a longer life expectancy than known air circuit breakers. Nevertheless, exemplary embodiments of the present disclosure are not only applicable to vacuum circuit breakers, but also to modern SF6 circuit breakers having a chamber filled with sulfur hexafluoride gas. Moreover, current interruption with vacuum means is one of the technologies used up to high voltage level. Modern vacuum circuit breakers improve the interruption process substantially through reduced contact travel, reduced contact velocity and small masses of moving electrical contact parts. These electrical contact parts can include special contact element arrangements, which are the subject of the present disclosure.
The U.S. Pat. No. 4,847,456 discloses a vacuum interrupter having a pair of inner electrical contact parts, which are in the form of RMF (Radial Magnetic Field) contact elements, which are surrounded by outer electrical contact elements. The outer electrical contact elements are connected electrically in parallel, and arranged closely adjacent to the inner electrical contact elements. One of the inner electrical contact elements is mounted such that it can move in the axial direction while the corresponding outer electrical contact element is immovably (e.g., stationary) mounted. Both outer electrical contact elements of the corresponding electrical contact parts are in the form of AMF (Axial Magnetic Field) contact elements. During a disconnection process, a contracting, rotating arc is struck between the inner electrical contact elements and is then commutated from the inner to the outer electrical contact elements. This results in the initially contracting arc between changing to a diffuser which burns between the AMF-like electrical contact elements until it is quenched. This solution allows a high disconnecting rate in a vacuum interrupter chamber.
The WO 2006/002560 A1 discloses an electrical contact arrangement and a vacuum interrupter chamber of the type mentioned initially, which also allows an increased switching rate. In particular, a high-short circuit disconnection capacity with a high arc burning voltage is disclosed.
The known contact arrangement for a vacuum interrupter chamber has a pair of inner electrical contact elements which are in the form of RMF contact elements and a pair of outer electrical contact elements. The outer electrical contact elements are connected electrically in parallel with the inner electrical contact elements and are arranged closely adjacent to the inner contact elements. At least one of the inner electrical contact elements is mounted such that it can move axially. The outer electrical contact elements are also in the form of RMF-like contact elements. The inner electrical contact elements are disc-shaped. The inner and the outer electrical contact elements are arranged and designed in such a manner that an arc which is struck during the disconnecting process between the inner electrical contact elements can be commutated entirely or partially between the outer electrical contact elements. That contact arrangement has a low resistance and is able to carry high currents.
As already mentioned, the arc can commutate onto the outer electrical contact elements. Whether one or two arcs burn, depends on the current level. After the disconnection of the initially touching electrical contact elements on load, a concentrated disconnection arc occurs first of all. In the case of an RMF like contact element, as the electrical contact elements open further a contracted arc is formed between the contact pieces. As the contact separation increases further during the course of the disconnecting process, a partial commutation or, with an appropriate physical design, a complete commutation occurs. If the arc—which has been struck between the inner contact pieces—commutates completely onto the outer electrical contact elements, then the interrupter chamber can carry and switch at least the same current as the interrupter chamber with only one RMF-like contact element pair.
The vacuum interrupter chamber which symmetrically surrounds the inner electrical contact parts is cylindrically shaped. One electrical contact part is mounted such that it can axially move while the corresponding electrical contact part is immovably mounted. The outer electrical contact elements of both electrical contact parts are provided with slots, so that they can form an RMF-like contact element. Thus, when a current is flowing through the outer electrical contact elements, a radially magnetic field is produced. The inner electrical contact elements of both corresponding electrical contact parts are also RMF-like contact elements and are provided with slots for the same purpose.
That special electrical contact design increases the production effort substantially. On the other hand it is necessary that the heat arising during the arcing phase is widespread on the electrical contact elements in order to achieve high current interruption performance.